In recent years, there has been drastic progress in high-speed information transmission networks along with worldwide diffusion of small portable devices. Under these circumstances, demands for small non-volatile memories of large capacities are increasing rapidly. Among them, NAND flash memories and small HDDs (hard disk drives), in particular, have made rapid progress in recording density and are used for various purposes such as memories for mobile music markets, memories for recording portable games, memory devices for personal computers, and so forth. However, it is said that these non-volatile memories have limitations in the degree of high-density recording.
Against this background, various memories have been proposed as next-generation non-volatile memory devices including one utilizing a phase change, one utilizing a magnetic change, one utilizing a ferroelectric substance, one utilizing a resistance change, and so forth. Among them, a resistance change type memory or a so-called ReRAM (resistive random access memory) is highly expected for reduction in power consumption and drastic improvement in read/write speed as compared to conventional memories by virtue of microfabrication.
A resistance change type material which is to serve as a memory portion is located between two electrodes in this ReRAM. It is important to realize an oriented structure of the memory portion in order to improve durability and characteristics of the ReRAM.
Such electrodes typically are formed of an electrically isotropic metal, a single crystal substance such as Si, or a metal compound in a similar state. On the other hand, such a memory portion is typically formed of an oxide layer having a polarity. Therefore, it is essential to orient the metal oxide or the like having electrical polarity on the nearly electrically isotropic electrodes, while maintaining conductivity between the electrodes and the memory portion. However, there are no conventional techniques known to achieve this configuration. Accordingly, in the conventional ReRAM, the memory portion is less oriented, resulting in poor durability and performance.